A contact lens directly contact an eyeball, such that it is required to maintain transparency and surface wettability while simultaneously maintaining eye safety and efficacy, and thus, oxygen needs to be appropriately supplied from the atmosphere, and carbon dioxide needs to be properly released from a cornea.
In addition, the contact lens needs to have a tear layer with smooth flow, and should be designed in consideration of a clinical aspect so as to avoid excessive friction between an eyelid and an eye surface. Further, the contact lens should satisfy conditions such as tensile strength of a material, biocompatibility, non-toxicity, optical transparency of a material, refractive index, surface wet ability, water content appropriate for the cornea, a welling rate, oxygen permeability, etc., to be used.
In general, the contact lens may be largely divided into a hard contact lens and a soft contact lens according to the material, and is classified for vision correction, treatment, cosmetic contact lens, etc., according to function. A hydrogel is a typical material of a soft contact lens that is used for purposes such as vision correction, treatment, etc. Here, most of the hydrogel contact lenses include silicone-based or acrylate-based materials as a main material.
The cornea of a human eye has no blood vessels, and has a structure in which oxygen is directly received from the external environment. However, when the contact lens is worn, the lens itself acts as a kind of barrier, which reduces oxygen permeability. A number of people prefer to wear a general hydrogel contact lens due to comfort wearability when it is worn, but the hydrogel contact lens has problems such as hypoxia (corneal edema) due to a low oxygen permeability and reduction in the wettability of a lens surface due to leaking components attached to the lens surface. Accordingly, the hydrogel contact lens requires not only superior wearability but also a high oxygen permeability, wettability, etc.
For example, when the silicone-based hydrogel contact lens is worn, oxygen is sufficiently supplied to the eye, and thus, a side effect of the corneal edema due to the hypoxia is not caused.
However, the silicone-based hydrogel contact lens has low wearability. That is, due to properties of the silicone-based hydrogel material, as a silicone content is increased, the oxygen permeability is sufficiently increased, but hydrophilicity of the lens surface is reduced. Accordingly, the silicone-based hydrogel material causes discomfort, and has problems such as eye irritation, corneal staining, attachment of the lens to the cornea, etc.
In order to overcome these disadvantages, Korean Patent No. 10-0594414 (Patent Document 001) used a method of increasing hydrophilicity by plasma surface treating the lens surface in initial first-generation silicone hydrogel contact lens products. However, this method still has low surface wettability, which causes discomfort to a wearer, and further includes a complicate process which is called a plasma surface treatment in a manufacturing process, which causes an increase in production costs.
Further, Korean Patent No. 10-0748379 (Patent Document 002) suggested a wettable silicone hydrogel lens according to Johnson & Johnson as a second-generation silicone-based hydrogel contact lens. The second-generation silicone-based hydrogel contact lens is manufactured by using a polyvinyl pyrrolidone (PVP) polymer as an internal wetting agent to increase wettability and a water content without the plasma post-processing step. However, the internal wetting agent (PVP) has worse wearability as it is slowly released out of the lens, and thus, the second-generation silicone-based hydrogel contact lens still has discomfort when it is worn.
Meanwhile, Korean Patent Laid-Open Publication No. 10-2007-0067679 (Patent Document 003) suggested a contact lens according to Asahi Kaei Aime Co., and CooperVision as a third-generation silicone-based hydrogel contact lens. The third-generation silicone-based hydrogel contact lens is manufactured by synthesizing a silicone macromer having hydrophilic property to a raw material itself. However, a high level of molecular design and a synthesis technique for the raw material are required.
Further, there are problems in that a manufacturing method for a raw material includes complicated various stages, and accordingly, stimulating residues in manufacturing the raw material are left in a final product.
In addition, a technology of increasing surface wettability has been attempted in the acrylate-based hydrogel contact lens. For example, Korean Patent No. 10-1249705 (Patent Document 004) suggested a method of modifying a contact lens surface by immersing the contact lens in an oligosaccharide solution. However, the method has a problem in that the oligosaccharide does not have sufficient physical and chemical binding force with a polymer matrix, which is released out of the lens surface.